Ink compositions enabling writing of dates and the like on plastic bags and ultrathin transparent films for food product packaging (wrap) containing food products to be stored are known, and examples of such known ink compositions include an ink composition for a writing tool comprising at least: a water-soluble dye; an alcohol-soluble and poorly water-soluble resin contained in an amount 3 times or more the water-soluble dye in the weight ratio; and water contained in an amount twice or more and 34 times or less the water-soluble dye in the weight ratio (Patent Literature 1).